Calipers must be off the car, on the bench to perform components replacement. Here is the step by step instruction:
Link title says for RB calipers, but is also a general guide for all fixed pistons...

From all of us at RacingBrake, we like to extend our congratulations and best wish for a lot of lucks with this first HBK (Huge Brake Kit), the largest brake kit ever built for Mercedes and any other...